+2
−1
Loading
Gitlab 现已全面支持 git over ssh 与 git over https。通过 HTTPS 访问请配置带有 read_repository / write_repository 权限的 Personal access token。通过 SSH 端口访问请使用 22 端口或 13389 端口。如果使用CAS注册了账户但不知道密码,可以自行至设置中更改;如有其他问题,请发邮件至 service@cra.moe 寻求协助。
We can starve out the transaction commit with a bunch of caching threads all
running at the same time. This is because we will only drop the
extent_commit_sem if we need_resched(), which isn't likely to happen since we
will be reading a lot from the disk so have already schedule()'ed plenty. Alex
observed that he could starve out a transaction commit for up to a minute with
32 caching threads all running at once. This will allow us to drop the
extent_commit_sem to allow the transaction commit to swap the commit_root out
and then all the cachers will start back up. Here is an explanation provided by
Igno
So, just to fill in what happens in this loop:
mutex_unlock(&caching_ctl->mutex);
cond_resched();
goto again;
where 'again:' takes caching_ctl->mutex and fs_info->extent_commit_sem
again:
again:
mutex_lock(&caching_ctl->mutex);
/* need to make sure the commit_root doesn't disappear */
down_read(&fs_info->extent_commit_sem);
So, if I'm reading the code correct, there can be a fair amount of
concurrency here: there may be multiple 'caching kthreads' per filesystem
active, while there's one fs_info->extent_commit_sem per filesystem
AFAICS.
So, what happens if there are a lot of CPUs all busy holding the
->extent_commit_sem rwsem read-locked and a writer arrives? They'd all
rush to try to release the fs_info->extent_commit_sem, and they'd block in
the down_read() because there's a writer waiting.
So there's a guarantee of forward progress. This should answer akpm's
concern I think.
Thanks,
Acked-by:
Ingo Molnar <mingo@kernel.org>
Signed-off-by:
Josef Bacik <jbacik@fusionio.com>
Signed-off-by:
Chris Mason <clm@fb.com>
CRA Git | Maintained and supported by SUSTech CRA and CCSE